The term “organic electronic device” refers to a device requiring charge exchange between an electrode and an organic material by using holes and electrons. The organic electronic device may be largely classified into two types according to the operational mechanism. One type is an electronic device in which an exciton is formed in an organic material layer by photons provided from an external light source to the device, the exciton is divided into an electron and a hole, the electron and the hole are transported to respective electrodes to be used as a current source (voltage source). The other type is an electronic device in which a hole and/or an electron is injected into an organic material semiconductor forming an interface with an electrode by applying a voltage or current to two or more electrodes to allow the device to operate by means of the injected electron and hole.
Examples of the organic electronic device include an organic light emitting device, an organic solar cell, an organic photoconductor (OPC), and an organic transistor. The above-mentioned examples of the organic electronic device all require a hole injecting or transporting material, an electron injecting or transporting material, or a light emitting material in order to drive the device.
Hereinafter, the organic light emitting device will be described in detail. The hole injecting or transporting material, the electron injecting or transporting material, and the light emitting material of the above-mentioned organic electronic devices act like those of the organic light emitting device as described later.
Generally, organic light emission means that electric energy is converted into light energy by using an organic material. An organic light emitting device using the organic light emission phenomenon typically includes an anode, a cathode, and an organic material layer that is interposed between the anode and the cathode. The organic material layer is to have a multilayered structure made of different materials in order to improve efficiency and stability of the organic light emitting device. For example, the organic material layer may be formed of a hole injection layer, a hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injection layer. If voltage is applied between two electrodes in the organic light emitting device having the above-mentioned structure, a hole is injected into the organic material layer at an anode and an electron is injected into the organic material layer at a cathode. When the hole meets the electron, an exciton is generated, and light is generated when the exciton is converted into a bottom state. It is known that the organic light emitting device has properties such as self-light emission, high luminance, high efficiency, low driving voltage, wide viewing angle, high contrast, and high-speed response.
The materials used for the organic material layer of the organic light emitting device may be classified into a light emitting material and a charge transporting material, for example, a hole injecting material, a hole transporting material, an electron transporting material, and an electron injecting material according to the type of function. Further, the light emitting material may be classified into a high molecular weight type and a low molecular weight type according to a molecular weight and into a fluorescent material on the basis of a singlet excitation state of electrons and a phosphorescence material on the basis of a triplet excitation state of electrons according to the type of light emitting mechanism. Additionally, the light emitting material may be classified into a blue, green, or red light emitting material and a yellow or orange light emitting material required to ensure a better natural color according to a light emitting color.
Meanwhile, an efficiency of a device is lowered owing to maximum luminescence wavelength moved to a longer wavelength due to the interaction between molecules, deterioration of color purity, and reduction in light emitting efficiency when only one material is used as the light emitting material, and therefore, a host/dopant system may be used as the light emitting material for the purpose of enhancing color purity and light emitting efficiency through energy transfer. This is based on a mechanism where if a dopant having an energy band interval lower than that of a host constituting the light emitting layer is mixed with the light emitting layer in a small amount, an exciton that is generated from the light emitting layer is transported to the dopant to emit light at high efficiency. In this connection, since the wavelength of the host is moved toward the wavelength of the dopant, it is possible to obtain light having a desired wavelength according to the type of dopant.
In order to allow the organic light emitting device to fully exhibit the above-mentioned excellent characteristics, a material constituting the organic material layer in the device, for example, a hole injecting material, a hole transporting material, a light emitting material, an electron transporting material, and an electron injecting material should be essentially composed of a stable and efficient material. However, the development of a stable and efficient organic material layer material for the organic light emitting device has not yet been fully realized. Accordingly, the development of new materials is continuously desired. The development of such a material is equally required in the above-mentioned other organic electronic devices.